Aliphatic 1,3-diols, particularly 1,3-propanediol, have many applications as monomer units for polyester and polyurethane, and as starting materials for the synthesis of cyclic compounds. For example, CORTERRA® polytrimethylene terephthalate is a polyester characterized by outstanding properties that is made of 1,3-propanediol (hereafter PDO) and terephthalic acid. There is much interest in the art in finding new routes for synthesizing PDO that are efficient, economical, and demonstrate process advantages.
U.S. Pat. Nos. 3,463,819 and 3,456,017 teach the hydroformylation of ethylene oxide to produce 1,3-propanediol and 3-hydroxypropanal (hereafter HPA) using a tertiary phosphine-modified cobalt carbonyl catalyst. U.S. Pat. Nos. 5,256,827; 5,344,993; 5,459,299; 5,463,144; 5,463,145; 5,463,146; 5,545,765; 5,545,766; 5,545,767; and, 5,563,302, 5,689,016, all assigned to Shell Oil Company, disclose cobalt catalyzed hydroformylation of ethylene oxide.
U.S. Pat. No. 5,304,691, assigned to Shell Oil Company, discloses a method of hydroformylating ethylene oxide to 3-hydroxypropanal and 1,3-propanediol in a single step using an improved catalyst system comprising a cobalt-tertiary phosphine ligand in combination with a ruthenium catalyst. In '691 PDO and HPA are produced by intimately contacting an oxirane, particularly ethylene oxide (EO), a ditertiary phosphine-modified cobalt carbonyl catalyst, a ruthenium co-catalyst, and syngas (carbon monoxide and hydrogen) in an inert reaction solvent at hydroformylation reaction conditions. A PDO yield of up to 86–87 mole % is reported, using a catalyst comprising cobalt ligated with 1,2-bis (9-phosphabicyclononyl)ethane as bidentate ligand, and either triruthenium (0) dodecacarbonyl or bis[ruthenium tricarbonyl dichloride] as cocatalyst. Also see U.S. Pat. No. 5,304,686, assigned to Shell, which discloses the synthesis of 3-hydroxypropanal using a ditertiary phosphine-modified cobalt carbonyl catalyst and a catalyst promoter. In the aforementioned patents, where a phosphine ligand is employed, it is bound to cobalt carbonyl.
It is known that water extraction can recover HPA intermediate or PDO product from an non-water-soluble solvent system in a two-step process and that use of a lipophilic promoter (quaternary ammonium or phosphonium, or lipophilic amine) rather than a sodium salt allows a majority of the cobalt carbonyl catalyst to recycle with the organic solvent phase, as desired. See, for example, U.S. Pat. Nos. 5,463,144; 5,463,145; 5,463,146; 5,545,765; 5,545,766; 5,545,767; 5,563,302; 5,576,471; 5,585,528; 5,684,214; 5,689,016; 5,731,478; 5,723,389; 5,770,776; 5,777,182; 5,786,524; and 5,841,003, all assigned to Shell.
Copending commonly assigned U.S. patent application Ser. Nos. 09/808,974 and 09/963,068 disclose, inter alia, phosphine ligated bimetallic catalyst compositions useful in the one-step synthesis of PDO, and a process for one-step synthesis of PDO. In these references the phosphine ligands are bound to the ruthenium compound rather than the cobalt compound.
Ruthenium carbonyls modified with phosphine ligands are quite effective as catalyst complexes in the one-step synthesis of PDO. However, phosphine ligands are relatively expensive and, in some cases, catalyst recycle may fall short of optimal. At the same time, product selectivity may fall short upon repeated recycle. These observations have thus far made it rather prohibitive to use phosphine ligands in hydroformylation catalysts for commercial use. It would be extremely desirable if substantially less ligand were effective in a bimetallic catalyst complex for the one-step synthesis of PDO and if other modifications, such as water extraction, enhanced the use of a reduced ratio and contributed to efficient recycle.